In a wireless communication system, a first and a second node communicate over a time-varying radio channel h(t) in alternating time slots on the same carrier frequency. In a given time slot, one of the nodes, such as the first node, may send a transmission over the time-varying radio channel. When the other node, such as the second node, receives the transmission, it may at the same time estimate radio channel characteristics of the time-varying radio channel. As an example, the estimated radio channel characteristics such as amplitude and phase may assist in demodulation of the transmission received by the second node. The estimated radio channel characteristics may be obtained by measurements on pilot symbols, transmitted by the first node. Such channel estimates, or estimated radio channel characteristics, represent one form of channel state information. Known methods utilizing channel state information include time- and frequency-dependent scheduling, link adaptation, pre-equalization, time reversal, interference cancellation, dirty paper coding and the like.
However, the accuracy of the channel state information, or channel estimates, will become obsolete with time. Furthermore, the first node cannot obtain a channel estimate before or during the actual transmission. Therefore, the accuracy of the channel estimate may degrade at a rate that is proportional to the speed at which the first and/or second node moves. Typically, the first node will report channel quality information (CQI), or channel quality indicator, during its transmit time slot. This information is, however, delayed, i.e. the information is not available to the second node until, for example, at a following time slot. Typically, the delay is longer than to the following slot not only due to estimation, coding and decoding delay, but also due to longer reporting period than one time slot. In the case of multi-antenna transmission, the channel quality information may comprise a rank indicator and a precoder matrix indicator (PMI). The channel quality information may be wide-band average or frequency-selective averages over smaller bandwidths. In some systems, as mentioned above, the channel quality information may comprise measures derived from channel estimates (causing information loss) to reduce signalling overhead, while in other systems the channel quality information may be sampled versions of the channel estimates.
In order to improve accuracy of the channel state information, it is known to configure the first node to employ so called channel prediction. Channel prediction may be that the first node observes the channel estimates, obtained using reported channel quality information during a time window [t0−T, t0] and uses this observed information to form an estimate of the channel at a future time instant t0+dt. Various methods for forming the estimate of the channel, including linear predictors or filters as well as model-based estimators, exist.
In many scenarios, known methods for estimation, or prediction, of channel state information are not sufficiently accurate. This may cause performance of the wireless communication system to degrade. Therefore, there is a need for an improved method for estimating channel state information.